1. Field of the Invention
The present invention relates to a device for positioning objects within a sealed chamber, specifically to such a device which combines rotary and translatory motions and can move samples within a vacuum deposition chamber or can transfer samples from one vacuum chamber to another.
2. Description of Prior Art
It is often desirable or necessary to move objects within a closed chamber, such as a vacuum chamber. Such movement usually is done by a shaft, which extends into the chamber so that translatory and rotary motions can be imparted into the chamber via the shaft from outside the chamber. The chamber should remain sealed at all times so as to constitute a closed system.
This is especially true in vacuum chambers where it would be clearly impractical to shut the system down merely to rotate the shaft or move it in an axial direction.
One example of the need to move objects within a vacuum chamber occurs when it is necessary or desirable to change the position of a semiconductive substrate or test specimen with respect to a measuring instrument or ray emitting device, such as an electron beam gun located in predetermined axial and angular positions with respect to a substrate in the chamber. Feedthrough mechanisms or manipulators were known to be used in the past for these purposes.
One such mechanism, which is shown in FIG. 1, is described in U.S. Pat. No. 4,768,911 to V. Balter, 1988. This Balter mechanism comprises a tubular housing 12 made from a magnetically permeable material. Housing 12 is closed at one end and open at the other end for attachment to a vacuum chamber 18 through an appropriate seal 21. Located inside housing 12 is a shaft 40, which has a square cross section. One end of shaft 40 is rotatingly connected to an inner permanent magnet 66, which can rotate with respect to shaft 40, but moves axially together therewith. Inner magnet 66 interacts with an outer magnet 70, which is slidingly installed on the outer surface of housing 12. The other end of shaft 40 protrudes into vacuum chamber 18 and may carry a specimen, such as a silicone substrate S, or another object to be accurately positioned and treated in vacuum. Shaft 40 is supported inside the housing by a bevel gear 32, which has a square opening 38 for guiding the above-mentioned square shaft during its axial movements. Gear 32 is a part of an angular feedthrough mechanism 80, which has another bevel gear 98 engaged with gear 32. Feedthrough mechanism 80 has its drive element outside the housing. Angular feedthrough mechanism 80 is used for imparting rotary motion to shaft 40. Movement of outer magnet 70 along tubular housing 12 transmits axial movements to shaft 40 via inner magnet 66 attached to this shaft. This device can transfer a specimen from one chamber to another by axial movement of shaft 40 and can position the specimen in either chamber in any desired axial and angular orientation for treatment or measurement.
However, the angular feedthrough mechanism 80, which is used in the Balter system, occupies useful space and limits the amount of axial movement of the specimen. In addition, the system has only two degrees of freedom (i.e., one axial and one rotary) and moves only the specimen. In some cases, however, it may be required to impart motions not only to a specimen, but also to an actuating mechanism, such as a clamping member, which can rotate with respect to a specimen, while the latter rotates and can be axially moved relative to the clamping member.
Another disadvantage of the Balter mechanism is that it has a sliding movement which involves surface-to-surface friction. After many cycles of operation of the device, such friction causes wear of contacting parts so that accuracy of operation of the mechanism can be impaired and worn-off particles may adversely contaminate a specimen of high purity, e.g., a semiconductor wafer.